This patent application is related to co-pending U.S. application entitled INTEGRATED CIRCUIT WITH CURRENT LIMITED CHARGE PUMP AND METHOD, Ser. No. 09/705,355 filed Nov. 3, 2000.
This invention relates generally to the field of integrated circuits and more particularly to integrated circuits having a charge pump.
A charge pump may be any two-port circuit that transforms electrical energy supplied to an input port at one voltage level into electrical energy delivered to an output port at a second voltage level. Many charge pumps contain at least one capacitor and at least two switches coupled together so that periodic operation of the switches alternately charges and discharges the capacitor(s) and transfers energy from the input port to the output port.
Because charge pumps ordinarily do not contain inductive elements (except as parasitic elements), the change transfer process is inherently dissipative. The energy efficiency of the pump equals the ratio of the energy delivered by the charge pump to the load divided by the energy supplied to the charge pump.
Many charge pumps are designed to provide an output voltage larger than their input voltage. A charge pump of this type will provide the maximum possible output voltage when unloaded. A charge pump whose maximum possible output voltage equals twice the input voltage is called a doubler; one whose maximum possible output voltage equals thrice its input voltage is called a tripler, and so forth. Because of the effects of output loading, and because of parasitic losses within the pump, charge pumps rarely, if ever, supply their full theoretical output voltage. For charge pumps with an output voltage larger than the input voltage, the voltage conversion efficiency (or voltage efficiency) of a charge pump may be defined as the ratio of the actual output voltage of the pump divided by the maximum output voltage of an unloaded idealized version of the pump.
Many practical charge pumps use diodes to implement one or more switches.
The forward voltage drops of these diodes reduce the charge pump""s voltage efficiency. Integrated diodes may also suffer from parasitic transistor action due to minority carrier injection that diverts a portion of the current flowing through them to the substrate, causing a further loss in energy efficiency.
In order to avoid the limitations of diode-based charge pumps, some charge pumps use MOSFET transistors to implement some or all of the switches. Gate drive circuitry generally complicates these circuits to an undesirable degree. The gate drive circuitry also draws energy from the pump, reducing its overall energy efficiency.
One aspect of the invention is an integrated circuit comprising a first node and a first stage charge pump coupled to the first node and to load circuitry. The first stage charge pump comprises a first capacitor coupled to a first signal source, a second capacitor coupled to a second signal source, a drain of a first n-channel field effect transistor coupled to the first capacitor, and a source of the first n-channel field effect transistor coupled to the first node. A source of a first p-channel field effect transistor is coupled to a second node and a gate of the first p-channel field effect transistor is coupled to the second capacitor. The gate and drain of the first p-channel transistor are coupled to the gate and drain of the first n-channel transistor, respectively. The charge pump also comprises a source of a second n-channel field effect transistor coupled to the first node, a drain of the second n-channel field effect transistor coupled to the second capacitor, and a gate of the second n-channel transistor coupled to the first capacitor. A source of a second p-channel field effect transistor is coupled to the second node, and a drain of the second p-channel transistor is coupled to the second capacitor. The gate and drain of the second p-channel transistor are coupled to the gate and drain of the second n-channel transistor, respectively.
The invention provides several important technical advantages. Various embodiments of the invention may have none, some, or all of these advantages. The invention may improve the voltage and energy efficiency compared to existing charge pumps. The invention avoids the forward voltage drop and minority carrier injection problems of typical diode designs. Further, the invention may be used at high frequencies with minimal voltage and/or energy efficiency losses. The invention may also reduce the die area required to implement the charge pump. The invention also may reduce energy and voltage efficiency losses due to parasitic capacitance in existing designs. The invention also allows the construction of multi-stage charge pumps using relatively low-voltage transistors. The invention can also be used to step down the input voltage to provide a lower output voltage, step up the voltage, or to invert the polarity of the input voltage.